In order to improve user experience, modern glass-ceramic cooktops are equipped with signal lamps or 7-segment displays. Here, the cooking surface itself is composed of a transparent, colored glass-ceramic panel (substrate), which usually appears black in top view. The signal lamps provide the user with information concerning the ON status of the cooktop or individual cooking zones, the control setting and also whether the cooking zone is still hot after it is turned OFF. LED lamps are usually employed as lighting means.
Based on the coloring of the glass-ceramic cooktop and the very limited selection of colored LED displays, the range of colors that are available for user information is very greatly limited. These displays are by default red or perhaps orange, which is also based on the coloring of the glass-ceramic cooktop. In DE 100 52 370.6, the transmission curve is described for a glass-ceramic cooktop that also permits, in particular, a transmittance for blue light at approximately 450 nm and thus an expanded capability for color display. In DE 10 2009 013 127.2, different display possibilities based on these glass ceramic products are indicated. By broadening the transmission spectrum also to the blue wavelength region, the color possibilities for displays have in fact been expanded, but based on the small number of different-color LED displays, the number of colors visible to the user is also limited in the case of these glass-ceramic cooktops. A white LED, for example, would be perceived by the user as having a clear yellowish tinge due to the transmission curve of the cooktop. In DE 10 2010 061 123.9, it is proposed to avoid this deficiency by the use of RGB-LEDs. An LED lamp is thus composed of three LEDs in the primary colors of red, green and blue. Corresponding to the transmission of the glass-ceramic cooktop, the intensity of the 3 color LEDs is adjusted so that a white color for the light signal is perceived overall by the observer. This technology requires three LEDs and the controls belonging to them. Color shifts may occur over long periods of use due to the different aging of the LEDs of different colors.